1. Field of the Invention
The invention concerns a tunneling machine for boring a tunnel, with a shield that can be driven into the soil and in which a cutting wheel, powered and equipped with ripping tools, is arranged.
2. Description of the Invention
Tunneling of this type are known and feature a cutting wheel with several cutting arms, where the ripped soil proceeds through the spaces in the cutting arms into the tunneling machine and is then removed. Owing to the high forces which occur, the hub area of the cutting wheel, originating from which the cutting arms extend radially outward, is of a massive and stabile design. Therefore, soil ripped in the area of the longitudinal axis of the cutting wheel needs to be moved in the radial direction of the cutting wheel up to one of the spaces between the cutting arms of the cutting wheel. Besides, since in the center area of the cutting wheel the velocity of the ripping tools contained there is lower than the velocity of the tools revolving on a larger radius, a dead core results often in the axis area of the cutting wheel, with essentially a soil displacement taking place there, instead of an active soil removal. The formation of a soil plug thus increases the forward resistance of the tunneling machine, especially in cohesive soil, such as loam and clay. To improve the escape of the soil in the dead core of the cutting wheel, slip layers have already been used. But these wear quickly, so that an initially slight forward resistance will in the course of time increase, due to the wear in the central area of the cutting wheel. The increased forward resistance with the prior tunneling machines reduces the rate of advance in tunneling and requires higher driving capacities.
The problem underlying the invention is to provide a tunneling machine which is characterized by a low forward resistance.